2.7 SPECTRA Flashcards
Irradiance of light
I=P/A where A area in m2
Irradiance of laser light
light from laser is monochromatic, coherent, forms a parallel beam
why does irradiance matter?
to understand the activity of the Sun and climate and to research the impact of solar activity on the Earth’s climate
How to improve the quality of the experiment of investigating irradiance?
- Darken the room. Place the light a distance from lamp
- Mearsure the distance between the objects
- Repeat these measurements for different distances
the graph of average irradiancde
against 1/d2 is a straight line
hence I1d1(squared)=a constant
I1d12=I2d22
A point source is one
which irradiates equally in all directions, which is a sphere
hence A=4pir2
ex; Sun or lamp
A laser is not a point source
and its irradiance doesn’t follow the inverse square law
An emission spectrum is
the range of colours given out/ emitted by a light source
Kinds of emission spectra
- Continious
- Line
Continuous spectrum
produced when white light is passed through a grating or prism
All frequencies of radiation (colours) are present
Line Spectrum
produced by light from a star or an electrical discharge lamp containing vapour of elements (пари елементів) such as sodium or mercucy
Consist of bright lines which are produced by electrons making transition from a higher energy level to lower
The** number of lines** in the spectrum corresponds to the number of possible transitions
An instrument which spreads light out into its wavelengths, creating a spectrum
spectroscope and spectrometer
Bohr Model of the Atom
A model of the atom which describes the arrangement of electrons (розташування) within it.
It proposes that electrons are in circular orbits around the nucleus which correspond to the energy level
The electrons can only occupy discrete energy levels, ground state or an excited state
energy level diagram
a diagram used to study the movement of electrons between energy levels in the atom
Ground state Eo
the lowest energy orbit
Excited state
an energy level above the ground state
electrons can move into it when they gain energy
Ionisation level is
the highest energy level
where E=0
all excited states
have negative energy level
Electron transition is
the movement of an electron from one energy level to another
ENERGY LEVEL (falling electron)
E2- E1=differenceE=hf
when the electron drops the energy is released
in the form of a** photon** where its energy and frequency are related by the energy difference btween two levels
atomic fingerprint
is a spectra of the element
how bright line is depends on
the number of photons emitted
to be excited the electron should be
heated (discharged tubes)
high voltage (filament lamps)
nuclear fusion (stars)
wavelength of red and violet
red 400nm
violet 700nm
in the continiuous spectrum the electrons
are not free, are shared between atoms resulting in a large numer of possible energy levels
PHOTON EMISSION
occurs when an electron drops from a higher energy level to a lower energy level
only photons with energies exactly matched to the difference between two energy levels can be emittedВипромінюється
Photon Absorption
an electron will move to the** higher** energy level when it absorbs the energy of a photon
Only photons with same matching energies can be absorbed(Поглинається)
Absorption Spectrum
produced when light with countinious spectrum passes through a low-pressure gas
they appear as black lines on countinuous spectrum
FORMULAR; E2=E1+hv (frequency)
Frauhofer lines
absorption lines in the spectum of the **sunlight **
they provide evidence for the composition of the Sun’s outer (зовнішній) atmosphere
